Commercial devices are readily available for intermixing separate materials and dispensing the mixed product through a common spout. The devices vary based upon the composition of the materials to be mixed, their relative viscosity and the application for the intermixed product.
In the dental profession, the practice of combining polymerizable composite materials for use in filling tooth cavities or for forming dental restorations has become commonplace. In the past, polymerizable materials were combined into a homogeneous mass by a hand operation. This practice is not only time consuming but cannot assure their proper proportion. The volumetric proportion of the materials in the mixed product controls its physical properties and the required exposure time to provide adequate curing. Accordingly, mixing the materials automatically permits presetting the volumetric proportion to maximize the physical properties and provides control over the exposure time.
One commercially available device for intermixing two dental restorative resins and discharging the mixed product through a common discharge nozzle is shown and described in U.S. Pat. No. 4,538,920. The intermixing of the resinous material is accomplished by using a static mixing element located in the discharge nozzle. The operation of the static mixing element and the geometrical configuration of its mixing blades is based on earlier prior patent disclosures such as for example U.S. Pat. Nos. 3,286,992 and 3,664,638. In the aforementioned U.S. Pat. No. 4,538,920, the static mixing element is securely held in a fixed position in order to maintain a predetermined alignment of the first blade of the static mixing element relative to the two streams of resinous material. In accordance with the teaching of the patent, a fixed and predetermined alignment of the mixing element in a premixing chamber or exit conduit is necessary to achieve maximum mixing of the two streams of resinous materials in the discharge nozzle. A complex assembly of components is described to accomplish proper rotational alignment of the static mixing element. This complex assembly requires accurate alignment which is labor intensive and is, accordingly, relatively expensive to fabricate.